Method of forming patient-specific implant

ABSTRACT

Methods and apparatus are provided for forming a patient-specific surgical implant based on mold system. The apparatus comprises a forming tool and a mold that may be generated using imaging and processing techniques and rapid prototyping methods. The mold apparatus includes at least two non-adjacent surface features for securing an implant forming material (such as a titanium mesh) during the forming process, enabling the implant forming material to be stretched beyond its elastic and thus permanently deformed with the correct patient-specific curvature. The implant may include one or more anatomic surface features for guidance and registration when transferring the implant to a patient.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/353,925, titled “METHOD OF FORMING PATIENT-SPECIFIC IMPLANT WITHTOPOLOGICAL CONTOURS” and filed on Jun. 11, 2010, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND

The present disclosure relates to methods and apparatus for thefabrication of patient-specific implants using imaging data, and moreparticularly relates to the fabrication of patient-specific implants forthe reconstruction of defects of the skull and facial bones.

The surgical repair of a defect of the skull or facial bones can be atechnically difficult, laborious and time-consuming procedure, and theaccurate restoration of the missing anatomy can be particularlychallenging. The recent adaptation of computer assisted design and rapidprototyping technology is known to dramatically increase efficiency andimprove outcomes. Provided that the defect is stable, clearly definedand well visualized prior to surgery, computer modeling can be employedto generate a virtual 3D model of a patient-specific implant.

Titanium mesh in particular has proven to be effective clinically in thereconstruction of non load-bearing defects of the skull and facial bones(Kuttenberger and Hardt, J. CranioMaxfac. Surg., 2001; Schipper et al.,Eur. Arch. Otorhinolaryngol., 2004). The mesh provides a stable,permanent, biocompatible reconstruction which is well tolerated, evenwhen in direct contact with paranasal sinuses.

Titanium mesh is generally shaped free-hand by traditional manualforming and manipulation, or pressworking with a cavity and punch.Unfortunately, accurate restoration of missing anatomy is oftendifficult, and can be compromised by problems associated with forming astable molded implant and correctly positioning the implant. This isparticularly true when defects are large, involve complex contours orexist in limited access anatomical sites.

SUMMARY

Embodiments provided herein including methods and apparatus for forminga patient-specific surgical implant based on mold system. The apparatuscomprises a forming tool and a mold that may be generated using imagingand processing techniques and rapid prototyping methods. The moldapparatus includes at least two non-adjacent surface features forsecuring an implant forming material (such as a titanium mesh) duringthe forming process, enabling the implant forming material to bestretched beyond its elastic and thus permanently deformed with thecorrect patient-specific curvature. The implant may include one or moreanatomic surface features for guidance and registration whentransferring the implant to a patient.

Accordingly, in one embodiment, there is provided an apparatus forshaping an implant forming material into a surgical implant forcorrecting a defect in a skeletal region, the apparatus comprising: amold comprising a defect-free surface profile of the skeletal region;and; a forming tool having a negative surface profile relative to themold, such that the implant forming material is shaped into the surgicalimplant when the implant forming material is compressed between the moldand the forming tool; wherein at least one of the mold and the formingtool comprise two or more non-adjacent surface features; and wherein thesurface features are configured to locally secure the implant formingmaterial between the mold and the forming tool such that the implantforming material is permanently deformed under application of suitablepressure.

In another embodiment, there is provided an apparatus for shaping animplant forming material into a surgical implant for correcting a defectin a skeletal region, wherein the implant forming material supportslateral fluid flow when the implant forming material is compressedbetween two surfaces, the apparatus comprising: a mold comprising adefect-free surface profile of the skeletal region; and; a forming toolhaving a negative surface profile relative to the mold, such that theimplant forming material is shaped into the surgical implant when theimplant forming material is compressed between the mold and the formingtool; wherein one of the mold and the forming tool comprises a channel,the channel comprising an external port and an internal port, whereinthe internal port is in flow communication with the implant formingmaterial when the implant forming material is compressed between themold and the forming tool.

In another embodiment, there is provided an apparatus for shaping animplant forming material into a surgical implant for correcting a defectin a skeletal region, the apparatus comprising: a mold comprising adefect-free surface profile of the skeletal region; and; a forming toolhaving a negative surface profile relative to the mold, such that theimplant forming material is shaped into the surgical implant when theimplant forming material is compressed between the mold and the formingtool; and a reservoir positioned to immerse the implant forming materialin a liquid while the implant forming material is compressed between themold and the forming tool.

In another embodiment, there is provided a kit for forming apatient-specific surgical implant to correct a defect in a skeletalregion, the kit comprising an apparatus as described above; and theimplant forming material.

In another embodiment, there is provided a method of fabricating a moldsystem for shaping an implant forming material into a surgical implantsuch that the surgical implant has a curvature configured to correct adefect in a skeletal region, the method comprising the steps of:obtaining a digital image of the skeletal region; processing the digitalimage to obtain a three-dimensional model of the skeletal region;processing the three-dimensional model to obtain a defect-freethree-dimensional surgical model of the skeletal region; processing thedefect-free three-dimensional surgical model and generating a model ofthe mold system, wherein the mold system comprises a positive mold and anegative forming tool, such that the implant forming material is shapedinto the surgical implant when the implant forming material iscompressed between the mold and the forming tool; including two or morenon-adjacent surface features in one or more of the mold and the formingtool; and fabricating the mold system; wherein the surface features areselected to locally secure the implant forming material between the moldand the forming tool such that the implant forming material ispermanently deformed under application of suitable pressure.

In another embodiment, there is provided a method of generating asurgical implant for correcting a defect in a skeletal region during asurgical procedure, the method comprising the steps of: providing anapparatus as described above; positioning the implant forming materialbetween the mold and the forming tool, wherein the implant formingmaterial has a sufficient spatial extent to contact the surfacefeatures; and applying a compressive force to the mold and the formingtool to shape the surgical implant.

In another embodiment, there is provided A method of generating asurgical implant for correcting a defect in a skeletal region during asurgical procedure, the method comprising the steps of: providing anapparatus as described above, positioning the implant forming materialbetween the mold and the forming tool, wherein the implant formingmaterial has a sufficient spatial extent to contact the surfacefeatures; and applying a compressive force to the mold and the formingtool to shape the surgical implant.

In another embodiment, there is provided a method of generating asurgical implant for correcting a defect in a skeletal region during asurgical procedure, the method comprising the steps of: providing anapparatus including a mold system that incorporates a reservoir asdescribed above, wherein the implant forming material comprises apolymer; adding liquid to the reservoir, where a temperature of theliquid is suitable for softening the polymer; immersing the implantforming material in the liquid; and applying a compressive force to themold and the forming tool to shape the surgical implant.

A further understanding of the functional and advantageous aspects ofthe disclosure can be realized by reference to the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the drawings, in which:

FIG. 1 provides a flow chart illustrating a method of forming animplant.

FIG. 2 shows a mold system that incorporates surface features forstretching an implant forming material beyond its elastic limit.

FIG. 3 provides photographs of a mesh implant having additional groovecontours.

FIG. 4 illustrates a mold incorporating an outer lip for engaging andsecuring the mold forming material.

FIGS. 5 (a) and (b) illustrate mold systems in which pins are used tosecure a mesh for forming an implant.

FIG. 6 illustrates (a) a mold system including pins for securing a meshduring compression, (b) an overhead view of the mesh showing theretaining pins, (c) the compressed mesh, (d) the resulting formedimplant, and (e) the formed implant trimmed to a desired size.

FIG. 7 illustrates (a) a model of a patient's skull showing the plannedsurgical site and (b) the extent of the implant and planned surfacefeatures.

FIG. 8 shows (a) the boundary of artificial surface features and (b)anatomical forming contours.

FIGS. 9 (a)-(f) illustrate various types of artificial surface features.

FIG. 10 shows (a) a metal mesh implant forming material, (b) the formingtool of the two-part system, (c) the mold, (d) the mesh formed into a 3Dshape over the mold after the presswork forming step, (e) the trimmedimplant, and (f) the implant transferred to the patient skull.

FIG. 11 shows a mold system including a liquid bath for immersing theimplant in a fluid prior to or after compression.

FIG. 12 (a)-(l) illustrates various example embodiments of a mold systemfor contacting the implant forming material with a liquid before, duringor after compression.

FIG. 13 illustrates an example of a mold system including a mechanicalpress and a thermal bath.

FIG. 14 shows (a) an example of a cross-section of a formed meshindicating artificial and anatomic contours and (b) an illustration themesh following removal of the excess mesh leaving a conforming mesh tothe anatomy.

FIG. 15 shows (a) a 3D CT scan of a frontal skull defect prior tosurgery, (b) a photograph showing the fabricated mold and forming tool,and (c) the deformed mesh having a curvature conforming to that of themold.

FIG. 16 provides (a) an intra-operative photograph of the mesh securedto the frontal skull and (b) a post operative axial CT cross-sectionshowing formed mesh in place with restoration of the forehead contour.

FIG. 17 shows CT image data demonstrating mucocele (mass) erodingthrough skull from within, and (b) 3D CT showing a defect in the skull,but where further resection at time of surgery will be necessary (theexact defect region is unknown prior to surgery).

FIG. 18 shows (a) a mold of the patient-specific skull shape, with thedefect obliterated and restored to normal shape, and (b) the mold andforming tool of the two-part system.

FIGS. 19 (a) and (b) show photographs of the contoured mesh secured tothe patient's bone, and FIG. 15( c) shows the implant secured to thepatient's skull.

FIG. 20 provides images of an orbital reconstruction mold system and theimplant forming material before and after the forming process.

FIG. 21 shows (a) a pre-operative 3D CT scan demonstrating a tumor inthe right orbit and maxilla to be resected, where the resection marginis unknown pre-operatively, (b) a post-operative coronal CT scanillustrating the position (marked by arrow) of a mesh that was customformed, and (c) a post-operative 3D CT scan illustrating the position(marked by arrow) of the custom-formed mesh in three dimensions.

FIG. 22 shows an illustration of a mesh that is (a) formed on a moldnear an anatomical feature and (b-c) extended to overlap a portion ofthe anatomical feature for registration.

FIG. 23 illustrates an embodiment in which (a) a mesh is shown formedinto an implant on a mold, (b) a guide structure is added to the implantfor registration, and (c) the implant is indexed to the patient usingthe guide structure.

DETAILED DESCRIPTION

Various embodiments and aspects of the disclosure will be described withreference to details discussed below. The following description anddrawings are illustrative of the disclosure and are not to be construedas limiting the disclosure. Numerous specific details are described toprovide a thorough understanding of various embodiments of the presentdisclosure. However, in certain instances, well-known or conventionaldetails are not described in order to provide a concise discussion ofembodiments of the present disclosure.

As used herein, the terms, “comprises” and “comprising” are to beconstrued as being inclusive and open ended, and not exclusive.Specifically, when used in the specification and claims, the terms,“comprises” and “comprising” and variations thereof mean the specifiedfeatures, steps or components are included. These terms are not to beinterpreted to exclude the presence of other features, steps orcomponents.

As used herein, the term “exemplary” means “serving as an example,instance, or illustration,” and should not be construed as preferred oradvantageous over other configurations disclosed herein.

As used herein, the terms “about” and “approximately”, when used inconjunction with ranges of dimensions of particles, compositions ofmixtures or other physical properties or characteristics, are meant tocover slight variations that may exist in the upper and lower limits ofthe ranges of dimensions so as to not exclude embodiments where onaverage most of the dimensions are satisfied but where statisticallydimensions may exist outside this region. It is not the intention toexclude embodiments such as these from the present disclosure.

As used herein, the term “defect” refers to an anatomical region thatrequires replacement, covering, or reinforcement, including, but notlimited to, holes, fractures, tumors, and deformations. The anatomicregion may include, but is not limited to, bone structures such as theskull, jaw, limb, and hip. The exact size, shape and specific locationof the defect need not be known prior to surgery.

As used herein, the term “implant forming material” refers to anymaterial that may be formed by presswork to generate a surgicalprosthesis for a defect. The resulting implant may be secured byfastening to surrounding bone structures. Suitable implant materialsinclude, but are not limited to, biocompatible metal sheet and meshstructures such as titanium mesh, polymeric sheets such as PMMA,polyethylene, and PEEK, and polymeric resorbable materials such aspolylactic-coglycolic acid. The implant forming material mayalternatively comprise a hybrid composite polymer-metal structure, forexample, a titanium mesh coated with polyethylene such as the MEDPOR®TITAN™ sheets.

As used herein, the term “non-adjacent surface feature” refers to two ormore surface features that, when incorporated into a mold systemfabricated based on a 3D surgical model, locally secure an implantforming material and produce non-elastic deformation of the implantforming material during a pressworking step in which the implant isformed.

FIG. 1 provides a flow chart illustrating a method of forming a surgicalcranial implant according to one embodiment. It is to be understood thatembodiments described herein are not limited to cranial defects, and thescope of the embodiments as disclosed herein is intended to encompass awide range of surgical implants that involve the use of pressworking.

In step 100, a digital imaging system, such as a CT, MRI, or surfacescanner, is used to obtain a imaging data pertaining to the patient'scranial anatomy. The imaging step provides anatomical data both withinand beyond the region associated with a defect (or an anticipateddefect). The imaging data is then imported in step 105 into a standardimage format, such as the Mimics™ software platform (Materialise,Belgium). This enables the creation of a 3D model of the patientanatomy. The model may be created using known techniques, such as usingthe steps of thresholding, region growing and manual editing. Automaticthresholding may be performed to achieve a first approximation of thebony surfaces of the skull, followed by manual editing to obtain arefined model. Haptic modeling, for example using a modeling softwareplatform such as the PHANTOM™ Desktop Haptic Device, may be used tofurther refine the model.

Having obtained a digital 3D representation of the patient anatomy instep 105, a 3D surgical model is produced in step 110. For example, the3D surgical model may be produced using a 3D model editing softwarepackage such as Magics™ software package (Materialise, Belgium). The 3Dsurgical model provides a defect-free representation of the patientanatomy, and can be produced by any one of many known techniques. Forexample, the mirroring technique may be employed, where thenon-defective half of the skull is isolated, copied, and integrated toform a new defect-free representation using a subtraction step.Alternatively, the matching technique may be employed, where digitalanatomical data from reference subjects is searched to obtaindefect-free data that provides a suitable match with the patientanatomy.

Subsequently, in step 115, the 3D surgical model is used to produce adigital model of a two-part mold system including a positive mold and anegative forming tool. The digital data from the 3D surgical model isprovided to a suitable software platform (such as the software packageSurfacer™) for designing the mold and forming tool of the system. Thisenables the mold system to be designed stereolithographically. Thedevice consists of a positive and a negative form, in which the positiveform (i.e. punch or mold) corresponds to the patient's anatomy (forexample, a representation of the skull or facial bones). The negativeform (i.e. forming tool) provides a matching surface adjusted toaccommodate the thickness of the desired mesh. The mold and forming toolmay be offset by an appropriate thickness to accommodate the thicknessof the implant forming material. For example, in the case of a titaniummesh plate with a thickness of 0.5 mm, the profile of the mold is offsetby 0.5 mm.

A final step in the generation of a model of the two-part mold is theassessment of the model for sufficient surface features, and theoptional modification of the model for the inclusion of additionalartificial surface features beyond the defect region, as shown in step120. When incorporated into a mold system that includes a mold andforming tool, non-adjacent surface features that are beyond the defectregion provide significant benefits to the process of forming andmaintaining the curvature of the implant. In particular, provided thattwo or more surface features are suitably positioned outside of thedefect region and have a sufficient radius of curvature, the surfacefeatures will cause implant fixation during the forming step. Thisallows the mold to frictionally contact the implant forming material attwo or more non-adjacent locations, thereby enabling the stretching ofthe implant forming material during the pressworking process in whichthe curvature of the mold is transferred to that of the implant.

This key advantage of frictional and static contact between the mold andforming tool and the implant forming material enables the mold andforming tool to stretch the implant forming material beyond its elasticlimit during the forming process, which overcomes the elastic memoryeffect and generates a permanent curvature in the implant. Thenon-elastic deformation of the implant during the forming processtherefore avoids problems associated with elastic or memory shaperelaxation, which can cause a formed implant to relax to an incorrectsurface profile.

Surface features may be anatomic or artificial. Non-limiting examples ofanatomical surface features include rims such as the orbital rim, ridgessuch as the brow ridges, zygomatic processes, maxillary buttresses, andthe margin of the mandible. Artificial contours may comprise any shapethat provides a suitable frictional fixing of the implant formingmaterial during the forming process.

The two or more non-adjacent surface features are incorporated outsideof the defect region and positioned to cause the stretching of theimplant forming material across the defect region during a pressworkingstep. In some cases, there may already be two adjacent anatomicalsurface features, such as those associated with the orbital rim.However, in order to provide sufficiently opposing forces for stretchingof the implant forming material over the defect region, at least oneadditional surface feature should be present in a non-adjacent location.For example, if the defect region is on the top of the skull and themold already includes the brow ridges, an additional non-adjacentartificial surface feature may be located near the back of the skull.The inclusion of the additional surface feature in a non-adjacentlocation enables the stretching of the implant forming material over thedefect region, where the matching of the curvature to the patientanatomy is most critical.

After having ensured the presence of two or more non-adjacent surfacefeatures, the model of the two-part mold may then be utilized tofabricate the mold for forming the implant in step 125. The negativeforming tool may consist of one or more pieces as appropriate foroptimal mesh bending. In one embodiment, a forming liner made from adeformable material is used in conjunction with the mold. The linerallows for variable depth to compensate for variations in thickness ofthe implant forming material and to ensure that forming pressure isevenly distributed.

Having produced the two-part molded system, the implant forming materialmay be pressed within the mold and forming tool to produce an implanthaving the desired surface curvature. Centrifugal tension in combinationwith a compressive force applied to a planar mesh or other implantforming material allows permanent deformation into a 3D shape. Thespecific configuration of this 3D shape is dictated by the two-partmold. As noted above, the provision of the non-adjacent surface featuresenables the stretching of the implant forming material beyond itselastic limit during the presswork step, thereby providing a permanentlyshaped implant with the correct curvature. The implant forming materialused in this step has a spatial extent that is larger that the defectionregion and extends to the surface features. The larger spatial extent ofthe implant forming material is also useful in providing sufficient areafor the fixation of the implant to adjacent patient tissue such as bone.Compression of the mold and forming tool may be manual or by amechanical press. The mold components may further comprise an elasticsurface for improved stabilization and bending of the implant formingmaterial.

In a final step shown at 130, the implant may be trimmed to a desiredshape. The trimming of the implant may be performed prior totransferring the implant to the patient, or after having correctlyregistered and/or fixed the implant into the patient (optionally afterreceiving, intra-operatively, information regarding a desired size ofthe implant). In another embodiment, the mesh may be initially trimmedto a size that includes the surface features, positioned, and thenfurther trimmed to a final size. An example of a formed implant is shownin FIG. 14 (a), which provides an example of a cross-section of a formedmesh indicating artificial (600 and 610) and anatomic 620 features. FIG.14 (b) shows an illustration the mesh following removal of the excessmesh leaving a conforming mesh to the anatomy, wherein the contour 630is characteristic of the curvature describing the missing anatomy in adefect, such that the formed implant will confirm to the adjacentexisting anatomy. The lower portion shows an ¾ view of the top pieceafter trimming away the excess material, including the artificialcontours.

In one embodiment, anatomical surface features may be employed to aid inthe registration of the implant. The use of anatomical surface featuresfor inter-operative guidance and registration enables the correctplacement of the implant onto the patient anatomy, without having topre-form the implant to a specific spatial size. Specifically, theanatomical surface features allow the implant to be placed upon thepatient using a lock-and-key fitting approach.

In one embodiment, the mold and forming tool are provided as a kit thatoptionally includes the implant forming material. The mold and formingtool may be pre-sterilized. The mold system and a suitable implantforming material may then be used in a pre-operative or inter-operativesetting to produce formed implant that has a large spatial extent. Theimplant forming material may include a spatial area that extends to atleast one anatomical surface feature outside of the defect zone. Thisallows for the accurate guidance and registration of the implant duringa surgical procedure. If the anatomical contour exists well beyond thedefect region, the implant forming material may include a tabbedstructure to enable accurate placement with the minimum implant formingmaterial. An example of such an embodiment is illustrated in FIG. 22. InFIG. 22( a), a mesh is show that is placed near an orbital anatomicalfeature, and the arrows indicate the direction in which the mesh mayalternatively be extended for registration purposes. FIGS. 22 (b) and(c) show two different example implementations in which the mesh isextended and registered with the anatomical features.

The mold may also include non-topological surface anatomic features thatare clearly visible intraoperatively for indirect verification ofregistration. These include, but are not limited to, cranial suturelines and muscle attachments.

A guide piece may be employed to properly position the implant, wherethe guide piece contains features that match the underlying patientanatomy for registration and alignment. In one non-limiting example inwhich the implant has a mesh structure, the guide piece may be anadditional mesh structure that is contoured to the patient anatomy andattached to the implant. In another embodiment, the guide piece may be asolid molded structure that may be provided in a sterilized form, suchas molded plastic, that is contoured to the patient anatomy and issecured to the implant. The guide piece may be removably attached to theimplant for ease in removal after implant registration. In anotherembodiment, the guide piece may include protuberances or other featuresthat allow the guide piece to be handled with ease when registering theimplant to the patient.

FIG. 23 provides an example implementation of an implant thatadditionally includes a guide piece for registration and indexing. FIG.23( a) shows a mesh that is formed into an implant, where the implant isshown residing on the mold after the forming step. In FIG. 23( b), aguide piece is added to the formed implant, and the guide piece isregistered to an anatomical feature. The resulting implant and guidepiece may then be indexed to the patient, as shown in FIG. 23( c), wherethe guide piece may be conveniently employed for handling and forregistration. The guide piece may be removed after the implant issecured to the patient.

The guide piece may be manufactured from a sterilizable material. In oneexample, the guide piece is formed from the same material as the moldsystem. The guide piece may alternatively be formed from another othersuitable material, such as plastic or another piece of the implantforming material (e.g. mesh). In another example, one or more metalplates could be used to form an appropriate guide piece. The guide pieceis formed with a custom curvature to link to the fiducial anatomy (theorbital rim in this case), with at least one or more extensions to theimplant forming material. The guide piece may be held in place againstthe anatomy by one or more curved sections (for example, the hooksperpendicular to the orbital arch in FIG. 23). In cases where theimplant forming material is a mesh, the ends of the guides may bematched with pins or the like to connect and hold the mesh by frictionfit.

FIGS. 3 to 5 illustrate various non-limiting devices and methods forforming an implant with a mold system incorporating surface features.The mold system includes forming tool 200 and mold 205. Implant formingmaterial 210 is provided between forming tool 200 and mold 205, and isformed into a desired shape under a compressive force. FIG. 3 shows oneembodiment in which multiple surface features are incorporated into themold system. For each concave surface feature 215 in the forming tool,there exists a corresponding and mating convex surface feature 220 inthe mold piece. The presence of the surface features cause the implantforming material to be stretched and deformed during the pressworkingstep, thereby retaining the shape of the mold. In other exampleembodiments, the surface features in one component of the mold systemneed not have a corresponding feature in the other component. Forexample, a liner, such as a rubber liner, may be included that iscompressed along with the implant forming material, where the lineraccommodates surface features in one mold component.

In one embodiment, artificial contours may be added to cross the defectregion in addition to the periphery. For example, FIG. 3 provides animage of a mesh-based implant in which artificial radial contour grooveshave been included to assist in the inelastic deformation of the mesh inthe central region of the implant. Such artificial contours are designedto specifically introduce small grooves in the mesh shape that inducesadditional rigidity into the mesh.

In one example implementation, the grooves are positioned to extend theintrinsic mesh strength along directions that are approximatelyperpendicular to the principal surface curvature, acting as reinforcingspines in the mesh structure. The grooves may be positioned to extendthe intrinsic mesh strength along directions that are normal to the meshsurface. For example, the mold may include spines that run along curvedsurface to provide additional strength to compressive forceperpendicular to that surface. In one example, the grooves are shallowwith a depth of less than about 2 mm from the main surface. Such ashallow depth acts to prevent cosmetic changes to the desired anatomicshape. Similarly, the groove width may be less than 2 mm, as governed bythe mesh link intervals. In another example, two or more grooves may bealigned in intersecting directions to provide rigidity along differentdirections of the meshes.

FIG. 4 provides an embodiment in which the implant forming materialextends to the lower region of the mold, where it is clamped at 225between mating beveled surfaces in the forming tool and mold pieces oneither sides of the mold. FIGS. 5( a) and 5(b) illustrate embodiments inwhich the implant forming material includes a mesh, and where clampingpins 230 on either sides of one of the mold components are employed tosecure and stretch the mesh. As shown, the pins are may be incorporatedat beyond a corner at 90 degrees relative to the primary formingsurface, resulting in a flat section of the implant forming material 235that is secured by the corner and the pin.

According to different example implementations, the pins may be a solidextension of the mold material or a separate insert. For example, FIG. 5illustrates an embodiment of the pin shape that is compatible with aparticular mesh design. The pins may have different cross-sections andplacement to be compatible with the mesh shape. The pins can fit intothe holes designed for surgical fixation screws or in the interspacecreated by the mesh links. It is to be understood that the illustratedembodiment involving pins is merely one example of a surface projectionsuitable for engaging and retaining a mesh-based implant formingmaterial.

Although the artificial surface features shown in FIGS. 3 to 5 are shownas multiple divots with multiple point-like projections, it is to beunderstood that a wide variety of artificial surface features arecompatible with the present disclosure, provided that they havesufficient curvature to secure the implant forming material duringcompression. For example, an edge or lip may be used, in which a cusp isprovided in the mold, over which the implant forming material can befolded to initiate fixation. Once pressed, the sharp cusp acts to holdthe implant forming material in place as it is deformed. Alternatively,a groove may be incorporated into the mold, where the groove comprisesan indentation and matching ridge. The ridge is adjusted to accommodatethe thickness of the implant forming material within the groove. Thegroove may be a semicircular indentation with edges having a curvaturesufficient to induce fixation and deformation. In another non-limitingembodiment, the artificial surface feature may be an interdigitatedgroove comprising a set of teeth arranged in a row to induce evengreater fixation and stretching than the aforementioned smooth groove.Furthermore, as noted in FIGS. 5 and 6, pins matched to the holesize/spacing of a mesh may be employed to achieve rigid fixation.

Referring now to FIGS. 6( a)-(d), an example implementation of a moldsystem incorporating pins is provided, where the implant formingmaterial is a mesh. FIG. 6( a) shows a two-part mold system includingforming tool 200 and mold 205. Mesh 250 is pressed between forming tool205 and mold 205, and secured in place during the application of acompressive force by pins 260. Forming tool 200 includes a surfaceprofile 270 that is contoured to form a desired implant shape. Surfaceprofile 270 (and a matching inverse profile in mold 205) may includeanatomical or artificial surface features.

FIG. 6( b) shows a top view of mesh 250 after it is secured onto mold205, but prior to the forming step. In the example embodiment shown,mesh 250 is supported and secured by 6 pins 260, which fix portions ofthe mesh in place during the forming step and assist in producinginelastic deformation of mesh 250. The pressed mesh 255 is shown in FIG.6( c), which takes the shape of surface profile 270 while being securedby pins 260. The formed mesh 255 is shown after removal from the moldsystem in FIG. 6( d), which may be subsequently trimmed to provideimplant 258, as shown in FIG. 6( e).

Although the example embodiments shown in FIGS. 4 to 6 illustrateclamping or pinning structures at more than one position, it is to beunderstood that the mold system may include any combination of two ormore non-adjacent implant deforming features, where the implantdeforming features may include clamping features, pinning features, andtopological features.

FIGS. 7-10 further illustrate embodiments in which artificial surfacefeatures are employed to secure the implant forming material during theforming step. Referring to FIG. 7( a), a model of a patient skull 300 isshown in which a defect 305 is present. As discussed above, such a modelcan be obtained using imaging and subsequent image data processingmethods. FIG. 7( b) shows a defect-free mold 310 marked with plannedlocations of the extent of the defect 315, the boundary of an artificialsurface feature 320 around and outside of the defect region, and theboundary of an anatomical surface feature 325.

FIG. 8( a) illustrates the mold 310 augmented with an artificial surfacefeature comprising ridge 330. The ridge, placed outside of the defectregion 315, enables the implant forming material to be frictionallysecured and stretched during the forming step.

While the mold 310 includes an anatomical surface feature 325, it may beadvantageous to augment the anatomical surface feature with anadditional artificial surface feature 335, as shown in FIG. 8( b). Theadditional artificial surface feature provides increased purchase of themold against the implant forming material and enabling higher strain tobe applied to the implant forming material during the application of acompressive force.

FIGS. 9 (a)-(f) illustrate additional non-limiting variations ofartificial surface features that may be incorporated into the mold (andcorresponding forming tool). As shown in the Figure, the artificialsurface features may include dimple or raised point-like structures,long ridges, short ridges, and combinations thereof. The surfacefeatures may be arranged around the perimeter of the defect region inorder to provide optimal adhesion and substantially uniform strain. Thiscan be particularly advantageous in avoiding wrinkles and otherimperfections in the transferred curvature. The surface features may beformed as an integral part of the mold system, or may be attached to themold system after initial fabrication of the forming tool and mold.

FIG. 10 illustrates the steps in the forming process using a formingtool and mold incorporating artificial surface features. FIG. 10( a)shows a metal mesh 340 that is molded to form the final implant andFIGS. 10( b) and (c) show the forming tool 345, mold 350, and artificialsurface features 355 and 360. The forming tool 345 and mold 350 areemployed to compress and inelastically stretch mesh 340, therebyproducing contoured mesh 365 as shown in FIG. 10( d). FIGS. 10( e) and10(f) show the mesh trimmed to the appropriate size and transferred tothe patient.

Although the preceding embodiments have been illustrated involving theuse of mesh structures for the implant forming material, it is to beunderstood that a wide range of implant forming materials may beemployed without departing from the scope of the present disclosure.

In one embodiment, the mold system may be configured for the formationof an implant based on an implant forming material that may be formedunder compression after an initial thermal softening step. An example ofsuch an implant forming material is a composite mesh. Composite meshestypically consist of a metallic mesh substrate coated with a polymer. Anexample of a suitable polymer is porous polyethylene. Because of therigidity of the composite mesh at room temperature, the mesh does notbend well without added heat. Heating softens the polymer coating andallows it to deform without cracking.

FIG. 11 illustrates an example implementation of a mold system thatenables immersion of the implant forming material within a cooling orheating liquid to heat and/or chill the mesh. The mold system includesforming tool 400 and mold 410, which include corresponding negative andpositive surface profiles 415 and 417, respectively, for shaping theimplant forming material under a compressive force. Implant formingmaterial 420 (such as a composite mesh) is placed within upper recess422 of mold 410. Liquid with a temperature suitable for softeningimplant forming material 420 is introduced into mold 410 such that theliquid immerses implant forming material 420. The liquid may be asterile liquid, such as sterilized water.

After the liquid has contacted and softened implant forming material420, implant forming material 420 is compressed between forming tool 400and mold 410 under application of compressive force 425. As forming tool400 is brought into close proximity to mold 410, liquid residing in andbelow recess 422 is forced outwards and overflows into reservoir 435 ofouter housing 430.

The liquid may be heated to a suitable temperature prior to itsintroduction into mold 410. Mold 410 may include a heat source forheating the liquid. Suitable heating sources include resistive heatingelements and an external closed-loop liquid heat exchanger thatinterfaces with internal flow channels within mold 410. Additionally, athermal sensor may be included in mold 410 to provide a measurementsuitable for maintaining a desired liquid temperature (for example,under a feedback control scheme using an external controller orprocessor).

Once compressed, the formed implant may be immersed in a cooling liquid,such as chilled water, to harden or ‘freeze’ the implant to maintain thedeformed shape. This may be performed by removing the formed implant andimmersing or otherwise contacting it with cooling liquid, or bycontacting the formed implant with the cooling liquid after removing theforming tool, but before removing the formed implant from the mold. Theformed implant may subsequently be trimmed to a desired shape before orafter affixing it to a skeletal region on a patient.

Referring now to FIG. 12( a), an example implementation of a mold systemis shown where forming tool 400 includes fluid channel 440 having anexternal port 445 and an internal port 447. Heating liquid may beintroduced into external port 445, where it flows through forming tool400 and emerges from internal port 447 to contact implant formingmaterial 420 (internal port 447 is in flow communication with implantforming material 420 when implant forming material 420 is compressedbetween forming tool 400 and mold 410. In the embodiment shown, implantforming material 420 may be a mesh or other suitable porous materialsuch that liquid may permeate implant forming material 420 when it iscompressed, such that liquid introduced into external port 445 flowsthrough channel 440, emerges from internal port 447 to contact implantforming material 420, and flows through implant forming material 420,thereby heating implant forming material 420.

After having formed the implant, cooling liquid, such as chilled water,may be injected to harden or ‘freeze’ the formed implant to maintain thedeformed shape. For example, as the compression drops, the liquid canflow through the interspace between the formed implant and the moldsystem components to provide cooling. The formed implant may beextracted and trimmed to a desired size.

In one example implementation, as illustrated in FIG. 12( b), liquid maybe introduced into external port 445 under pressure, such that liquidflows through channel 440, emerges from internal port 447 to contactimplant forming material 420, and flows through implant forming material420, and overflows mold 410 into external reservoir 435 of outer housing430. A flow mechanism may be employed to recirculate the liquid fromreservoir 435 to external port 445. Suitable flow mechanisms includeautomated flow mechanism such as a pump, and manual flow mechanisms suchas a syringe.

In one embodiment, liquid may be reheated or cooled before beingreintroduced into port 445 under recirculation. By employing a porousimplant forming material that exhibits resistance to flow (for example,due to capillary forces within the implant forming material pores orchannels), a restoring fluid force is provided that acts to distributethe fluid within the implant forming material. Accordingly, asubstantial or complete amount of implant forming material 420 may beeffectively heated or cooled by the liquid.

FIGS. 12 (c) and (d) show alternative example embodiments involving amulti-channel structure 446 within forming tool 400, with and withoutexternal reservoir 430, respectively. Additional channels 446 may bebeneficial in providing more rapid and/or even liquid distribution.FIGS. 12 (e) and (f) show alternative example embodiments involving aporous internal structure 448 within forming tool 400, with and withoutexternal reservoir 430, respectively. Porous internal structure may bebeneficial in providing a larger thermal mass within forming tool 400,and generating a more even temperature distribution within implantforming material 420.

As shown in FIGS. 12 (g)-(i), one or more additional channels 450 may beprovided in mold 410, where additional channel 450 is shown having anadditional inlet port 452 in fluid communication with implant formingmaterial 420 when implant forming material is compressed between formingtool 400 and mold 410, and an additional external port 454. Additionalexternal port 454 may be in flow communication with reservoir 435, orwith an additional reservoir. As described above, a flow mechanism maybe employed to recirculate the liquid from reservoir 435 or fromadditional external port 454 to external port 445.

FIGS. 12 (j)-(l) illustrate alternative embodiments where external port460 exits forming tool 400 in a horizontal direction. A horizontalexternal port exiting mold 410 may also be employed in an alternativeembodiment of FIGS. 12 (g)-(i).

While FIG. 12 illustrates selected combinations of fluidic elements, itis to be understood that any or all of the features shown may becombined in a given implementation.

FIG. 13 illustrates an example implementation of a mold system thatincludes a two part mold 500, a thermal bath 530, and a mechanical press560. Two part mold 500 includes forming tool 505 and mold 510. Mold 510may include a slot 514 or other suitable feature for registering amating structure 516 in forming tool 505.

Thermal bath 530 includes a housing 535 for receiving and supportingmold 510, such that mold 510 may be filled with a thermal liquid tooptionally soften implant forming material 550 prior to compression. Inone embodiment, thermal bath 535 includes one or more retainingstructures, such as lateral retaining slots 540, for maintaining implantforming material in a submerged position prior to or during the formingprocess. Additional example retaining structures include hooks andflanges. Accordingly, implant forming material 550 is prevented fromexperiencing buoyant motion such as floating out of a suitable positionprior to or during the forming process.

Mechanical press 560 includes a vise having a rotatable handle 562connected to a threaded shaft 564 that is received within nut portion566 of fixture 568. Fixture 568 includes base portion 570 having recess572 for receiving thermal bath 535. Rotation of rotatable handle 562causes axial motion of platform 580, which applies a compressive forcebetween forming tool 505 and mold 510 when forming tool 505 and mold 510are seated in thermal bath 535.

Forming tool may be secured onto a lower portion of platform 580 byfingers 585 that are received within slotted portions 516 of formingtool 505. This enables implant forming material to be optionally heatedby a fluid in thermal bath 535 prior to contacting implant formingmaterial 550 between forming tool 505 and mold 510.

It is to be understood that anatomic and/or artificial surface featuresmay be incorporated into the embodiments illustrated in FIGS. 11, 12 and13.

In one embodiment, the implant forming material (such as a metal mesh,alloy mesh, or a composite polymer-metal mesh), the forming tool, andthe mold are sterile and/or sterilizable. In one embodiment, the moldsystem may be sterilized by disassembling the mold system andsterilizing each component. In an example implementation, a mold systemaccording to the aforementioned embodiments may be provided to form animplant forming material, such as a metal or composite mesh, into ashape that restores the boney surface of the orbital recess. Restorationof a fractured orbital floor is a common surgical task to which customimplants as disclosed herein are suitable. Of particular note is thecomplex curvature of the orbital floor that is generally a concavesurface that accommodates the bulk (globe) of the eye rising to a broadplateau as the orbital recess narrows behind the globe to support theligaments and central nerve bundle. Current restoration methods anddevices generally rely on manually bending flat meshes or highlyspecialized orbital floor plates. Unfortunately, it is difficult tomatch both the appropriate depth of concavity of the orbital base andthe rising plateau at the distal end of the orbital floor.

Using an implant formed according to the above embodiments, thecurvature of the original floor can be restored by creating a mirror ofthe unaffected orbit. Similarly defects of the roof, lateral and/ormedial walls of the orbit, combined defects of two or more contiguouswalls of the orbital cavity, can be reconstructed in this fashion.

The orbital forming mold system consists of two parts, one correspondingto the surface of the desired orbit surface and the other the negativeof that surface, offset by thickness of the mesh to be bent. Because ofthe curvature of the orbital rim, this anatomic feature serves as boththe registration and fixation surface for inducing inelastic deformationof an implant forming material such as a mesh. The distal portion of themesh can be bent over a sharp edge to induce tensile deformation undercompression, as illustrated in FIG. 5. Generally, the meshes employedfor orbital reconstruction are thinner than those used elsewhere in theskull. As a result, the two-piece orbital tool may be used with manualcompression. Alternatively, the mold system may be compressed in amechanical press for added compressive force, for example, asillustrated in FIG. 13.

The following examples are presented to enable those skilled in the artto understand and to practice embodiments of the present disclosure.They should not be considered as a limitation on the scope of thepresent embodiments, but merely as being illustrative and representativethereof.

EXAMPLES Example 1 Patient with Post-Infection Frontal Skull Defect

FIG. 15( a) shows a 3D CT scan of a frontal skull defect prior tosurgery. Prior to surgery, it was determined that further removal ofbone during the surgical procedure may be necessary to obtain clearmargins free of infection. The final defect size was therefore not fullydetermined prior to surgery.

The missing geometry in the forehead was modeled to generate a 3Dphysical prototype of the desired final skull shape according toaforementioned embodiment. The fabricated mold and forming tool areshown in FIG. 15( b). The mold comprises the virtually reconstructeddefect as well as the surrounding key anatomical features. The formingtool (shown on the left) conforms to the mold, and similarly extends tothe surrounding key anatomical features, well beyond the defect.

During the surgical procedure, titanium mesh was shaped between the moldand forming tool. Conforming mesh to anatomical landmarks beyond thedefect (in this case the eyebrow ridges and nasal root) ensures accuratespatial orientation and placement of the implant and stretching of themesh beyond its elastic limit during the forming process. FIG. 16( a)provides an intraoperative photograph of the mesh secured to the frontalskull. Forehead soft tissues have been stripped and reflected downwardsto expose the entire frontal skull. The location of the nasal root isindicated by the white arrow. The titanium implant has been fitted tothe eyebrow ridge contours and nasal root to ensure optimal positioningin the reconstruction of the defect. and FIG. 16( b) provides apost-operative axial CT cross-section showing formed mesh in place withrestoration of the forehead contour.

Example 2 Fronto-Orbital Skull Defect, Unknown Size and Shape

FIG. 17( a) shows a coronal CT cross-section demonstrating a large leftintracranial tumor, which is eroding through bone into the forehead(white arrow), and through the base of the skull into the left orbitalcavity (white star). FIG. 17( b) is a 3D CT scan in which the size ofthe skull defect prior to surgery is shown. The defect was expected tobe much larger following tumor resection, and accordingly it was notpossible to predict the ultimate size and shape of the defect prior tosurgery.

Virtual modeling of the desired skull and orbital shape in relation tosurrounding anatomy was completed to produce a physical prototype of thedesired final result. FIG. 18( a) and (b) show the fabricated mold andforming tool. Bilateral eyebrow ridges, nasal root, orbital cavities,serve as anatomical contours and skeletal references and assist inproviding permanent mesh deformation during forming.

The entire frontal bone is shown in FIG. 19( a), as seen from the front.The shaped titanium mesh implant restores skeletal continuity, integrityand symmetry to the forehead. FIG. 19( b) provides a view from below,where the shaped titanium implant has been conformed around the eyebrowridge and into the roof of the orbit. The frontal skull viewed fromabove is shown in FIG. 19( c). The root of the nose is at the bottom ofthe photo. Because the implant extends beyond the margins of the defectto unaltered anatomical reference points, optimal spatial orientationand position are ensured.

Example 3 Orbital Floor Defect

FIG. 20 provides a photograph of a mold system for the repair of anorbital defect using a mesh. The mold system includes forming tool 700and mold 705, which may be compressed (for example, manually compressed)to form composite mesh 710 into formed surgical implant 720.

The mesh employed in this example was a Medpor® composite mesh, and theimplant was formed using the system shown in FIG. 13. The mesh washeated in the hot water bath 535 to soften the mesh prior to compressionin the mold system. The water was heated to a near boiling temperature,but water was not boiling when the mesh was implant submerged. The meshmay also or alternatively be separately pre-heated prior to thecompression step.

The mesh was mounted in mold 510 and the forming tool 505 was alignedand mounted in mechanical press 560. The mechanical press 560 was closedand more hot water was injected into port 590 as the press wascompressed down on the forming tool assembly. The forming tool and moldwere fully compressed together to their limits and left in position.

After applying the compressive force, with the composite mesh compressedbetween the forming tool and the mold, cold water was injected throughport 590 in the mold system in order to harden the formed mesh.Alternatively, the entire assembly may be immersed in cold water.Finally, the forming tool and the mesh were separated, and the implantformed from the composite mesh was removed and trimmed to a desiredsize.

FIG. 21( a) demonstrates a tumor in the right orbit and maxilla to beresected, where the resection margin is unknown pre-operatively. Inparticular, the defect size, shape or location are unknown. FIG. 21( b)is a post-operative coronal CT scan illustrating the position (marked byarrow) of a mesh that was custom formed according the methods providedabove for restoring orbital continuity and anatomy on coronalcross-section. FIG. 21( c) is a post-operative 3D CT scan illustratingthe position (marked by arrow) of the custom-formed mesh in threedimensions.

The specific embodiments described above have been shown by way ofexample, and it should be understood that these embodiments may besusceptible to various modifications and alternative forms. It should befurther understood that the claims are not intended to be limited to theparticular forms disclosed, but rather to cover all modifications,equivalents, and alternatives falling within the spirit and scope ofthis disclosure.

Therefore what is claimed is:
 1. An apparatus for shaping an implantforming material into a surgical implant for correcting a defect in askeletal region, the implant forming material comprising a soliddeformable structure, said apparatus comprising: a mold comprising adefect-free surface profile of the skeletal region; and a forming toolhaving a negative surface profile relative to said mold, such that theimplant forming material is shaped into the surgical implant when theimplant forming material is compressed between said mold and saidforming tool; wherein at least one of said mold and said forming toolcomprise two or more non-adjacent surface features; and wherein eachsurface feature is configured to produce fixation of a portion of theimplant forming material at a location associated with said each surfacefeature when the implant forming material is compressed between saidmold and said forming tool, such that the implant forming material isstretched between said surface features and permanently deformed beyondits elastic limit under application of suitable pressure.
 2. Theapparatus according to claim 1 wherein one or more of said surfacefeatures comprises a surface projection.
 3. The apparatus according toclaim 2 wherein said surface projection is a pin.
 4. The apparatusaccording to claim 1 wherein one or more of said surface featurescomprises a surface contour.
 5. The apparatus according to claim 4wherein said surface contour comprises a radius of curvature sufficientto secure to locally secure the implant forming material such that theimplant forming material is permanently deformed under application ofsuitable pressure.
 6. The apparatus according to claim 1 wherein one ormore of said surface features are positioned outside of a regionassociated with said defect.
 7. The apparatus according to claim 1wherein one or more of said surface features are positioned, at least inpart, within a region associated with said defect.
 8. The apparatusaccording to claim 1 wherein said mold and said forming tool comprise apatient-specific surface profile.
 9. The apparatus according to claim 8wherein said patient-specific surface profile is based on imaging data.10. The apparatus according to claim 1 wherein a positive surfacefeature in one of said mold and said forming tool corresponds to anegative surface feature in the other of said mold and said formingtool.
 11. The apparatus according to claim 1 wherein one or more of saidsurface features comprises an anatomical surface feature.
 12. Theapparatus according to claim 11 wherein said anatomical surface featureis a rim or a ridge.
 13. The apparatus according to claim 12 wherein therim the orbital rim.
 14. The apparatus according to claim 12 wherein theridge is selected from the group consisting of brow ridges, zygomaticprocesses, maxillary buttresses, and a margin of a mandible.
 15. Theapparatus according to claim 11 wherein said anatomical surface featureis augmented with an artificial surface feature.
 16. The apparatusaccording to claim 1 wherein one or more of said surface featurescomprises an artificial surface feature.
 17. The apparatus according toclaim 16 wherein said artificial surface feature is selected from thegroup consisting of divots with corresponding projections, an edge overwhich the implant forming material may be folded and stretched, a grooveand matching ridge, and a groove comprising interdigitated teeth with amatching ridge.
 18. The apparatus according to claim 1 wherein one ormore of said mold and said forming tool further comprises an additionalanatomical feature for indirect verification of registration of theimplant forming material.
 19. The apparatus according to claim 18 wheresaid additional anatomical feature is selected from the group consistingof cranial suture lines and muscle attachments.
 20. The apparatusaccording to claim 1 wherein said defect is a cranial defect.
 21. Theapparatus according to claim 1 wherein one or more of said surfacefeatures is secured onto or recessed within said mold or forming tool.22. An apparatus for shaping an implant forming material into a surgicalimplant for correcting a defect in a skeletal region, the implantforming material comprising a solid deformable structure, wherein theimplant forming material supports lateral fluid flow when the implantforming material is compressed between two surfaces, said apparatuscomprising: a mold comprising a defect-free surface profile of theskeletal region; and; a forming tool having a negative surface profilerelative to said mold, such that the implant forming material is shapedinto the surgical implant when the implant forming material iscompressed between said mold and said forming tool; wherein one of saidmold and said forming tool comprises a channel, said channel comprisingan external port and an internal port, wherein said internal port is inflow communication with the implant forming material when the implantforming material is compressed between said mold and said forming tool;wherein at least one of said mold and said forming tool comprise two ormore non-adjacent surface features; and wherein each surface feature isconfigured to produce fixation of a portion of the implant formingmaterial at a location associated with said each surface feature whenthe implant forming material is compressed between said mold and saidforming tool, such that the implant forming material is stretchedbetween said surface features and permanently deformed beyond itselastic limit under application of suitable pressure.
 23. The apparatusaccording to claim 22 further comprising a reservoir in flowcommunication with a fluid overflowing from the implant forming materialwhen the fluid is injected into said external port.
 24. The apparatusaccording to claim 23 further comprising a flow mechanism in fluidcommunication with said external port and said reservoir.
 25. Theapparatus according to claim 22 wherein said channel is a first channelprovided within one of said mold and said forming tool, and whereinanother of said mold and said forming tool comprises a second channel,wherein said second channel comprises an additional external port and anadditional internal port, and wherein said additional internal port isin flow communication with the implant forming material.
 26. Theapparatus according to claim 25 wherein said additional external port isin flow communication with a reservoir.
 27. An apparatus for shaping animplant forming material into a surgical implant for correcting a defectin a skeletal region, the implant forming material comprising a soliddeformable structure, said apparatus comprising: a mold comprising adefect-free surface profile of the skeletal region; and; a forming toolhaving a negative surface profile relative to said mold, such that theimplant forming material is shaped into the surgical implant when theimplant forming material is compressed between said mold and saidforming tool; and a reservoir positioned to immerse the implant formingmaterial in a liquid while the implant forming material is compressedbetween said mold and said forming tool; wherein at least one of saidmold and said forming tool comprise two or more non-adjacent surfacefeatures; and wherein each surface feature is configured to producefixation of a portion of the implant forming material at a locationassociated with said each surface feature when the implant formingmaterial is compressed between said mold and said forming tool, suchthat the implant forming material is stretched between said surfacefeatures and permanently deformed beyond its elastic limit underapplication of suitable pressure.
 28. The apparatus according to claim27 wherein one of said mold and said forming tool comprises saidreservoir.
 29. The apparatus according to claim 27 wherein saidreservoir comprises one or more retaining structures for receiving theimplant forming material and preventing buoyant motion of the implantforming material when the implant forming material is contacted with theliquid.
 30. The apparatus according to claim 27 further comprising aheat source for heating the liquid in said reservoir.
 31. The apparatusaccording to claim 27 further comprising a first support for supportingsaid mold, a second support for supporting said forming tool, and apressure application means for compressing the implant forming materialbetween said mold and said forming tool.